[Moin-user] WikiSync is broken if backup/restore is used

Andrey Bondarenko abone27 at mail.ru
Tue Dec 14 06:59:58 EST 2010

First of all, I want to thank MoinMoin developers for the great
software. MoinMoin is the only tool I found suitable for handling
personal notes. I'm using it for a few years and can sey it is one of
the most valuable tool for me.

My usage patter of MoinMoin is rather specific. I keep there random
notes, but because I neet to access them on several computers that do
not have network access to each other, so I have to keep an autonomous
instance of MoinMoin on every host. I've tried to keep them in sync
using the following procedure.

Instances A and B needs to be synchronized, I create auxiliary wiki
instace M on a removable media (flash). Then I configure SyncJobs:
A <-> M and B <-> M. In theory, moving M between sites should allow
keeping A and B in sync. But, it seems, I found one corner case.

Mobile instance M is vulnerable to accidental loss, so I make frequent
backups. I thought, If I lose M, I may recover it from a recent backup
and that is OK, but current WikiSync implementation stores part of M
state (page revision numbers) in peer instances A, B. If M is restored
from backup this state information could become invalid. This may lead
to random stack traces (the best case) or silent data corruption
(worst case).

For example, some revisions that were in M before loss may not exist in
backup, this case leads to invalid FROM_REV and TO_REV stack

see http://www.moinmo.in/4ct10n/edit/MoinMoinBugs/1.9WikiSyncCorruptedSynctags

The other case, may happen if M loses some page revision, but
then gain it from the other source. This case leads to silent
page data corruption 

see. http://www.moinmo.in/MoinMoinBugs/1.9WikiSyncUnicodeDecodeErrorInMergeDiff

I think, the problem is hard to resolve and don't expect it will be
fixed soon, but, probably, we can put a word of warning to the docs,
that one should avoid use of WikiSync if he uses Backup/Restore?

Thank you.

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